The Encyclopedia of Cosmology

The following sections are included:

• Dedication
• Preface
• Acknowledgments
• Contents

The following sections are included:

• Astroparticle physics and cosmic energy pie
  • Atoms
  • Dark matter
  • Dark energy
• Cosmic history
• A survey of candidates for DM particles
  • WIMP miracle?
• The scope of this volume
• Notation
• References

The following sections are included:

• Basics
  • Friedmann–Lemaître–Robertson–Walker Universe
  • Energy forms
  • Future
  • Density perturbation
• Thermal production
  • Number density history
  • Decoupling temperature
  • Interaction and decay rates
• Cosmological nucleosynthesis
• Baryon number in the Universe
• Thermal WIMP production in the Universe
  • Heavy neutrino
  • Forces for weakly interacting massive particles
  • WIMP relic density
• Nonthermal production
  • Non-thermal WIMP production
  • E-WIMP production
  • ADM production
  • Axion production
  • Heavy lepton as WIMP
• References

Studying motion of galaxies in the Coma cluster, Zwicky suggested the existence of nonluminous mass at the cluster scale [1]. Nowadays, the nonluminous matter is called dark matter in the particle physics jargon. Dark matter (DM), being composed of very weakly interacting elementary (or composite) particles, must be present in all astrophysical scales, from the Universe of the horizon size down to solar and even down to Earth scales. In particle physics, DM candidates are broadly classified to the bosonic coherent motion (BCM) and weakly interacting massive particles (WIMPs), which will be theoretically presented in Chapters 4, 6 and 7. The detection strategy of DM at laboratories will be discussed in Chapter 9

After the discovery of neutron in 1932, Fermi introduced four-fermion interactions of electron, electron-type neutrino, proton, and neutron. With Fermi’s four-fermion interactions of 1934, there are 34 terms with 34 coupling constants. But, soon after the discovery of parity violation in weak interactions in 1956, it was established that the weak interaction was described by the four-fermion current–current interaction: the current of the form “V - A” with one coupling constant published in [1, 2] and talked earlier in [3].

During the Universe evolution, scalar fields separated more than the horizon scale at that epoch are not correlated, and the random vacuum expectation values (VEVs) of scalar fields settle to some topological defects at a later epoch when the cosmic temperature is lowered. The temperature forming these defects defines the critical temperature of forming the defects. Zero-, one-, and two-dimensional defects are called monopoles, strings, and domain walls, respectively. Also, Q-balls have been considered. A monopole, having a finite size, may be considered to be a three-dimensional object, but we can consider it an approximate point particle. The scale of the approximate point particle is the inverse VEV. In this sense, we may distinguish an approximate point-like monopoles from Q-balls. Q-balls carrying multiple global charges can be considered large, and they may be regarded as three-dimensional objects. Also, black holes can be considered large three-dimensional objects.

In this chapter, we discuss the bosonic collective motion (BCM). The BCM is a quite general concept. Since axion is the prototype model for the BCM, symmetry principles are the key to (almost) stable dark matter (DM) candidates. In this chapter, we discuss BCM arising from the approximate global symmetries, and in Chapter 7, we will discuss cold dark matter (CDM) from discrete symmetries. These symmetries are affected by gravity, which we call “gravity spoil” of symmetries. Gravity spoil of global symmetries has already been mentioned in the preceding chapter, and we will summarize it in Section 6.6 before using the discrete symmetries in Chapter 7.

Basics on the WIMP (weakly interacting massive particle) have been already discussed in detail at several places in this book, as presented in Chapter 2, and Sections 4.2, 4.5, 5.3, and 6.6. In fact, the main theme in the cold dark matter (CDM) discussion in this book, except the bosonic collective motion discussed in Chapter 6, is based on the WIMP idea. Therefore, here we will pay attention to the particle physics aspects on the particles useful for WIMPs and their possible interactions. This chapter is a brief summary of theories on WIMPs and E-WIMPs.

The origin of the baryon asymmetry of the Universe (BAU) has been a longstanding theoretical issue. The baryon number density n_B/n_γ ≃ 6.1×10⁻¹⁰ is one of the most accurately determined quantity in the precision cosmology, as sketched in Chapter 2. At the cosmic temperature above 1 GeV, numbers of baryons and antibaryons must be comparable to that of photons. But the present value of n_B/n_γ is extremely small O(10⁻⁹), implying a scenario that the Universe has started with the net baryon number almost zero before the nucleosynthesis era,

The following sections are included:

• Introduction
  • Bosons or fermions?
  • Local DM density
• Detection of nongravitational long range forces
  • Dark photon
  • The Cavendish-type experiments
• Detection of light pseudoscalars
  • Axion detection experiments
  • Laser searches
  • Solar axion search
  • Search for cosmic axions
• Massive particles
  • Collider search of massive DM particles
  • Indirect detection of WIMPs
  • Direct detection of WIMPs
• References

The following section is included:

• Index